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1.
Hydraulic and osmotic properties of spruce roots 总被引:9,自引:6,他引:3
Rdinger Marcus; Hallgren Stephen W.; Steudle Ernst; Schulze Ernst-Detlef 《Journal of experimental botany》1994,45(10):1413-1425
Hydraulic and osmotic properties of roots of 2-year-old Norwayspruce seedlings (Plcea abiea (L.) Karst) were investigatedusing different techniques (steady flow, pressure probe, andstop flow technique). Root pressures were measured using theroot pressure probe. Compared to roots of herbaceous plantsor deciduous trees, excised root systems of spruce did not developappreciable root pressure (-0.001 to 0.004 MPa or -10 to 40cm of water column). When hydrostatic pressure gradients wereused to drive water flows across the roots, hydraulic conductivities(Lpr) were determined in two types of experiments: (i) rootpressure relaxations (using the root pressure probe) and (ii)steady flow experiments (pneumatic pressures applied to theroot system or xylem or partial vacuum applied to the xylem).Root Lpr ranged between 0.2 and 8108m s1 MPa1(on average) depending on the conditions. In steady flow experiments,Lpr depended on the pressure applied (or on the flow acrossthe roots) and equalled (0.190.12) to (1.21.7)108m s1 MPa1 at pressures between 0.2 and 0.4 MPaand (1.51.3)108 m s1 MPa1 at appliedpressures between 0.8 and 1.0 MPa. When pressures or vacuumwere applied to the xylem, Lpr values were similar. The hydraulicconductivity measured during pressure relaxations (transientwater flows) was similar to that obtained at high pressures(and water flows). Although there was a considerable scatterin the data, there was a tendency of the hydraulic conductivityof the roots to decrease with increasing size of the root system.When osmotic gradients were used to drive water flows, Lpr valuesobtained with the root pressure probe were much smaller thanthose measured in the presence of hydrostatic gradients. Onaverage, a root Lpr=0.017108 was found for osmotic andLpr=6.4108 m s1 MPa1 in correspondinghydrostatic experiments, i.e. the two values differed by a factorwhich was as large as 380. The same hydraulic conductivity asthat obtained in osmotic experiments using the pressure probewas obtained by the 'stop flow techniquel. In this technique,the suction created by an osmoticum applied to the root wasbalanced by a vacuum applied to the xylem. Lpr values of rootsystems did not change significantly when measured for up to5 d. In osmotic experiments with different solutes (Na2S04,K2S04, Ca(NO3)2, mannitol), no passive uptake of solutes couldbe detected, i.e. the solute permeability was very low whichwas different from earlier findings on roots of herbs. Reflectioncoefficients of spruce roots (O were low for solutes for whichplant cell membranes exhibit values of virtually unity ( 相似文献
2.
Effects of a Range of O2 Concentrations on Porosity of Barley Roots and on their Sugar and Protein Concentrations 总被引:1,自引:0,他引:1
Barley was grown at a range of oxygen concentrations (0.59mg l1), in nutrient solutions. Growth of both shootsand seminal roots was restricted by O2 concentrations lowerthan 23 mg l1) but nodal root growth was not. Root porosities were increased even at those O2 concentrationswhich did not restrict growth, and were inversely proportionalto the protein levels of the roots. Sugar concentrations increasedappreciably only at those O2 concentrations which also restrictedgrowth. Hordeum vulgare L., barley, root porosity, sugar, protein, oxygen concentration 相似文献
3.
ITO OSAMU; OKANO KUNIO; KUROIWA MIYOKO; TOTSUKA TSUMUGU 《Journal of experimental botany》1985,36(4):652-662
Ten-day old kidney bean plants (Phaseolus vulgaris L. cv. Shin-edogawa)were exposed to 2.0 and 40 parts 106 NO2, and0.1, 0.2, and 0.4 parts 106 O3 alone or in combinationfor 2, 4, and 7 d. The effects of these air pollutants wereexamined with respect to the growth, partitioning of assimilates,nitrogen uptake, soluble sugar content, and root respiration. Decreased dry matter production was significant with all treatmentsexcept 2.0 parts 106 NO2 and 0.1 parts 106 O3.Exposure to mixtures of the gases produced more severe suppressionof growth than exposure to the single gases. Root/shoot ratiowas significantly lowered at 7 d by the gas treatments otherthan 2.0 parts 106 NO2 and 0.1 parts 106 O3. Thetotal nitrogen content of plants was increased by all treatments;the higher percent of nitrogen found with O3 exposure will resultfrom the growth retardation which increases the concentrationof nitrogen in the plants because the absorption of nitrogenby roots was unaffected. The combination of O3 with NO2 significantlydecreased the assimilation of NO2 by the plants. The concentration of soluble sugars in roots was decreased bythe gas treatments. There was a strong positive correlationbetween soluble sugar content and dry weight of the roots harvestedat 7 d. Root respiration was relatively unchanged until 5 dand then decreased significantly at 7 d by 2.0 parts 106NO2 and 02 parts 106 O3. Retarded growth of theroots and the decreased root respiration may be due to diminishedtranslocation of sugars from leaves to roots caused by exposureto air pollutants. The uptake of soil nitrogen was not closelyrelated with root respiration in the case of O3 exposure. Key words: NO2, O3, Phaseolus vulgaris, Growth, Sugars, Root respiration 相似文献
4.
Cutler Horace G.; Crumley Farrist G.; Cox Richard H.; Wells John M.; Cole Richard J. 《Plant & cell physiology》1984,25(2):257-263
Cyclopenin (C17H14O3N2) and cyclopenol (C17H14O4N2), isolatedfrom an abberent strain of Penicillium cyclopium (NRRL 6233),significantly inhibited the growth of etiolated wheat (Triticumaestivum) coleoptile segments. The former inhibited at 103and 104 M, the latter at 103 M. Cyclopenin producedmalformation of the first set of trifoliate leaves in bean (Phaseolusvulgaris) at 102 M and necrosis and stunting in corn(Zea mays) at 102 M. Cyclopenol induced no apparent effectsin bean or corn plants. Neither compound changed the growthor morphology of tobacco (Nicotiana tabacum) plants. Cyclopenininduced intoxication, prostration and ataxia in day-old chicksat 500 mg/kg, but they recovered within 18 hours. Cyclopenolwas inactive against chicks when dosed at levels up to 500 mg/kg. (Received October 11, 1983; Accepted December 15, 1983) 相似文献
5.
Kim Daekyung; Nakashima Takuji; Matsuyama Yukihiko; Niwano Yoshimi; Yamaguchi Kenichi; Oda Tatsuya 《Journal of plankton research》2007,29(3):241-247
Raphidophycean flagellates, Chattonella marina and C. ovata,are harmful red tide phytoplankters; blooms of these phytoplanktersoften cause severe damage to fish farming. Previous studieshave demonstrated that C. marina and C. ovata continuously producereactive oxygen species (ROS) such as superoxide anion (O2)hydrogen peroxide (H2O2) under normal growth conditions, andan ROS-mediated toxic mechanism against fish and other marineorganisms has been proposed. Although the exact mechanism ofROS generation in these phytoplankters still remains to be clarified,our previous study suggested that NADPH oxidase-like enzymelocated on the cell surface of C. marina may be involved inO2 generation. To investigate the localization of O2and H2O2 generation in C. marina and C. ovata, we employed 2-methyl-6(p-methoxyphenyl)-3,7-dihydroimidazo[1,2-a]pyrazin-3-oneand 5-(and-6)-carboxy-2',7'-dichlorodihydrodihydrofluoresceindictate, acetyl ester, which are specific fluorescent probefor detecting O2 and H2O2, respectively. Observationby fluorescence microscopy of live phytoplankters incubatedwith each probe revealed that O2 is mainly generatedon the cell surface, whereas H2O2 is generated in the intracellularcompartment in these phytoplankters. When the cells were rupturedby ultrasonic treatment, O2 levels of C. marina and C.ovata decreased significantly, whereas a few times higher levelsof H2O2 were detected in the ruptured cell suspensions whencompared with the levels of the live cell suspension. In immunoblottinganalysis, the protein recognized by anti-human gp91 phox wasdetected in both species. These results suggest that, in bothphytoplankters, the underlying mechanisms of O2 and H2O2generation may be distinct and such systems are independentlyoperating in the cells. 相似文献
6.
Kinetics of Root Elongation of Maize in Response to Short-Term Exposure to NaCl and Elevated Calcium Concentration 总被引:9,自引:0,他引:9
CRAMER GRANT R.; EPSTEIN EMANUEL; LAUCHLI ANDRE 《Journal of experimental botany》1988,39(11):1513-1522
To study the effect of salt (NaCl) on root elongation we developeda device that measures this effect by means of a Linear VariableDifferential Transformer (LVDT). To test the efficacy of thedevice we performed experiments demonstrating that (a) ratesof elongation of primary maize (Zea mays L.) roots were comparableto elongation rates of primary roots growing freely in solutionculture; and (b) chilling and low O2 concentrations of the solutionelicited the expected responses. Inhibition of root elongation by 75 mol m3 NaCl was gradual.At an iso-osmotic concentration, mannitol did not inhibit rootgrowth, suggesting that the inhibition was not due to osmoticfactors but rather to effects of salt on metabolism. The additionof supplemental Ca (10 mol m3) ameliorated this stressfulcondition. Timing of the application of Ca was critical. Treatmentwith Ca after addition of NaCl only partially restored growth,but pretreatment with Ca completely prevented the inhibitionof growth by salt stress. Key words: Root growth, Zea mays L., salinity 相似文献
7.
The CO2 compensation point at 25 °C and 250 µEinsteinsm2 s1 wasmeasured for 27 bryo-phyte species, andwas found to be in the range of 45160 µl CO2 I1air. Under the same conditions Zea mays gave a value of 11 µlI1 and Horde um vulgare 76 µI1. The rate of loss of photosyntheticallyfixed 14CO2 in the light and dark in six bryophytes (three mosses,two leafy liverworts, one thalloid liverwort) was determinedin CO2-free air and 100% O2. The rate of 14CO2 evolution inthe light was less than that in the dark in CL2-free air, butin 100% O2 the rate in the light increased, so that in all butthe leafy liverworts it was greater than that in the dark. Raisingthe temperature tended to increase the rate of 14CO2 evolutioninto CO2-free air both in the light and dark, so that the light/dark(L/D) ratio did not greatly vary. The lower rate of loss of14CO2 in the light compared tothe dark could be due to partialinhibition of dark respiration reactions in thelight, a low rate of glycolate synthesis and oxidation, or partialreassimilation of the 14CO2 produced, or a combination of someor all of these factors. 相似文献
8.
Lamaze, T., Sentenac, H. and Grignon, C. 1987. Orthophosphaterelations of root: NO3effects on orthophosphate influx,accumulation and secretion into the xylem.J. exp. Bot.38: 923934. Orthophosphate (Pi) accumulation by barley (Hordeum vulgareL.) roots was specifically inhibited by NO3 as comparedto Cl and SO42 , and Pi secretion into the xylemwas stimulated. The inhibition of Pi accumulation by NO3was also observed in roots of intact photosynthesizing horsebean(Vicia faba L.), rice (Oryza sativa L.) and soybean (Glycinemax L.) plants. NO3 effects on Pi transport by rootswere more thoroughly investigated with corn (Zea mays L.). Theywere due to intracellular NO3. Pi secretion was stillstimulated by NO3 after Pi withdrawal from the absorptionsolution. 32Pi influx decreased during Pi accumulation, supportingthe hypothesis that this ion allosterically regulated its owntransport system by feedback control. This control was modulatedby other anions: the decrease was more pronounced in the presenceof nitrate. Chronologically, the depressive effect of NO3on 32Pi influx appeared after the inhibition of Pi accumulation.Furthermore, under conditions where Pi accumulation was notaffected by NO3, 32Pi influx and Pi secretion into thexylem became insensitive to the presence of nitrate. Our hypothesisis that the stimulative effect of NO3 on Pi secretionand the depressive one on 32Pi influx are the repercussionsof an increase in the Pi cytosolic concentration due to an NO3-induced decrease in Pi uptake by the vacuoles. Key words: Root, orthophosphate fluxes, orthophosphate accumulation, nitrate, ionic interaction 相似文献
9.
Millhouse, J. and Strother, S. 1987. Further characteristicsof salt-dependent bicarbonate use by the seagrass Zostera muelleri.J.exp. Bot. 38: 10551068. The contribution of HCO3to photosynthetic O2 evolutionin the seagrass Zostera muelleri Irmisch ex Aschers. increasedwith increasing salinity of the bathing seawater when the inorganiccarbon concentration was kept constant. K1/2 (seawater salts)for HCO3 -dependent photosynthesis was 66% of seawatersalinity. Both short- and long-term pretreatment at low salinitiesstimulated photosynthesis in full strength seawater. Twentyfour hours pre-incubation of seagrass plants in 3·0 molm3 NaHCO3 resulted in increased photosynthesis at allsalinities, apparently due to stimulation of HCO3 use(K1/2 (seawater salts) = 26%). Vmax (HCO3) was not affectedby low salinity pretreatment. The kinetics of HCO3 stimulationby the major seawater cations was investigated. Ca2+ was themost effective cation with the highest Vmax (HCO3) andwith K1/2(Ca2+) = 14 mol m3. Mg2+ was also very effectiveat less than 50 mol m3 but higher concentrations wereinhibitory. This inhibition cannot be accounted for solely byprecipitation of MgCO3. Na+ and K+ were both capable of stimulatingHCO3 use. Stimulation was in two distinct parts. Up to500 mol m3, both citrate and chloride salts gave similarresults (K1/2(Na+) 81 mol m3, Vmax(HCO3) 0·26µmol O2 mg1 chl min1), but use of citratesalts above 500 mol m2 caused a second stimulation ofHCO3 use (K1/2(Na+) 830 mol m3, Vmax(HCO3)0·68 µmol O2 mg1 chl min1). Vmax(HCO3)for the second-phase Na+ or K+ stimulation was of the same orderas for Ca2+-stimulated HCO3 use. To further characterizesalt-dependent HCO3 use, the sensitivity of photosynthesisto Tris and TES buffers was investigated. The effects of Trisappear to be due to the action of Tris+ causing stimulationof HCO3 -dependent photosynthesis in the absence of salt,but inhibition of HCO3 use in saline media. TES has noeffect on photosynthesis. External carbonic anhydrase, althoughimplicated in salt-dependent HCO3 use in Z. muelleri,could not be detected in whole leaves. Key words: Zostera muelleri, HCO3 use, salinity 相似文献
10.
The Combined Effects of Salinity and Root Anoxia on Growth and Net Na+ and K+-accumulation in Zea mays Grown in Solution Culture 总被引:2,自引:0,他引:2
The effects of excess salinity and oxygen deficiency on growthand solute relations in Zea mays L. cv. Pioneer 3906 were examinedin greenhouse experiments. The roots of plants 14 d old growingin nutrient solution containing additions of NaCl in the range1.0200 mol m3 were either exposed to a severedeficiency of O2 by bubbling with nitrogen gas (N2 treatment),or maintained with a supply of air (controls), for a periodof 17 d. The threshold NaCl concentration resulting inappreciable inhibition of leaf extension, and shoot f. wt gainin controls was between 10 and 25 mol m3. At 25 mol m3NaCl the ratio of Na+/K+ transported to shoots was about 20times greater than in plants in 1.0 mol m3 NaCl. Theeffect of addition of NaCl to the nutrient solution was to enhanceNa+ movement but simultaneously depress the rate of K+ transportto shoots (per g f. wt roots). Interactions between NaCl levels and aeration treatment wereshown by analyses of variance to be statistically significantfor leaf extension, shoot and root f. wt gains, Na+ and K+ concentrationsin shoots and roots. When roots were N2-treated, shoot and rootgrowth were depressed, the effect of aeration treatment beinggreatest at NaCl concentrations of 50 mol m3 or less.Additionally, N2-treatment greatly accelerated Na- transportto shoots while depressing K+ transport still further, so thatat 10 mol m3 NaCl the ratio Na+/K+ acquired by the shootswas 230 times greater than in controls. Over the concentrationrange 1.0 to 50 mol m3 NaCl, the ratio Na+/K+ transportedto shoots by anoxic roots increased by a factor of 860. Mechanisms controlling changes in solute flux to the shoot,and the significance in relation to plant tolerance of excesssalts or oxygen deficiency are discussed. Anaerobic, corn, flooding, maize, oxygen-deficiency, salinity 相似文献
11.
This paper reports the effects of low O2 concentration (001,0055, and 0.115mol m3) in nutrient solutions onK+/Na+ selectivity of growing and mature root tissues of 6-to 8-d-old, intact, wheat (Triticum aestivum cv. Gamenya) seedlings. Increases in anaerobic catabolism and decreases in O2 uptake,K+ uptake and K+/Na+ selectivity were all more pronounced and/oroccurred at higher external O2 concentrations in the apex (02mm) than in the expanding tissues (24 mm); these growingtissues were, in turn, more affected than the expanded tissuesof the roots (412 mm). Selectivity for K+ over Na+ in roots and shoots was particularlysensitive to O2 deficiency. For example, in apical tissues (02mm) K + /Na+ selectivity was already reduced at 0.115 mol m3O2, yet at this O2 concentration there was no effect on eithergrowth or (K+/Na+) uptake. Upon transfer from 0.01 to 0.26 mol m3 O2, a detailedstudy of the 12 mm root tips showed that 70% of these tips regainedhigh (K+ + Na+) concentrations and K+/Na+ ratios. In contrast,there was no recovery in the remaining 30% of the 12 mm roottips. Net K+ transport to the shoots during the period afterre-aeration was negative for the population as a whole. Theseverity of these effects supports the view that the root tipsand the stele were more susceptible to O2 deficiency than wasthe cortex of the fully-developed root tissues. Key words: Hypoxia, K+/Na+ selectivity, expanded and expanding tissues 相似文献
12.
The use of chlorate as an analogue for NO3 during nitrateuptake into Chara corallina cells has been investigated. NO3inhibits 36C1O3 influx into Chara over the concentrationrange 01000 mmol m3. Lineweaver-Burke plots ofthe data are characteristic of competitive inhibition by NO3in the low concentration range (0300 mmol m3 ClO3)and apparent KINO3 is 140 mmol m3 which is of a similarorder of magnitude as apparent KmCIO3- 180 mmol m3. Athigher substrate concentrations the inhibition by NO3was not characteristic of competitive or uncompetitive inhibition. 36C1O3/NO3 influx was dependent on K+ and Ca2+in the external medium and inhibited by FCCP. NO3 pretreatmentor N starvation increased subsequent 36C1O3/NO3influx into Chara. A comparison between rates of net NO3uptake and 36C1O3/NO3 influx supported the previoushypothesis that NO3 efflux is an important componentin the determination of overall uptake rates. Key words: Nitrate, Chara, 36CIO3 相似文献
13.
Inoculation with Azospirillum lipoferum Affects Growth and Gibberellin Status of Corn Seedling Roots
Maize (Zea mays L., hybrid Cargill 147) seedlings, grown inaseptic conditions, were inoculated with three strains of Azospirillumlipoferum (Al op 33, Al iaa 320, and ATCC 29708) or culturedin different concentrations of indol-3-acetic acid (IAA) orgibberellin A3 (GA3). After 48 h, root length, root surfacearea, root dry weight, and shoot dry weight were measured inall treatments. Gibberellin content was evaluated in selectedroots of control and Azospirillum inoculated seedlings by gaschromatography-mass spectrometry-selected ion monitoring withthe use of deuterated gibberellins as internal standards. Thethree strains of A. lipoferum, IAA (2 ng ml1), and GA3(40 to 400 pg ml1) significantly enhanced root growth.Improvement of root hair growth and density was obtained mainlywith A. lipoferum strain Al op 33 and GA3 40 pg ml1.GA3 was identified by gas chromatography-mass spectrometry (byboth, full scan and selected ion monitoring) in a free acidfraction from roots of the seedlings inoculated with A. lipoferum.In the roots of the non inoculated seedlings GA3 was found afterhydrolysis of a fraction expected to contain glucosyl conjugates. (Received April 26, 1993; Accepted September 27, 1993) 相似文献
14.
Water Influx Characteristics and Hydraulic Conductivity for Roots of Agave deserti Engelm. 总被引:4,自引:0,他引:4
NOBEL PARK S.; SCHULTE PAUL J.; NORTH GRETCHEN B. 《Journal of experimental botany》1990,41(4):409-415
Various plant and environmental factors influence the hydraulicproperties for roots, which were examined using negative hydrostaticpressures applied to the proximal ends of individual excisedroots of a common succulent perennial from the Sonoran Desert,Agave deserti Engelm. The root hydraulic conductivity, Lp, increasedsubstantially with temperature, the approximately 4-fold increasefrom 0.5°C to 40°C representing a Q10 of 1.45. Suchvariations in Lp with temperature must be taken into accountwhen modelling water uptake, as soil temperatures in the rootzone of such a shallow-rooted species vary substantially bothdaily and seasonally. At 20°C, Lp was 2.3 x 107 ms{macron}1MPa{macron}1for 3-week-old roots, decreasing to abouthalf this value at 10 weeks and then becoming approximatelyhalved again at 6 months. For a given root age, Lp for rainroots that are induced by watering as lateral branches on theestablished roots (which arise from the stem base) was aboutthe same as Lp for established roots. Hence, the conventionalbelief that rain roots have a higher Lp than do establishedroots is more a reflection of root age, as the rain roots tendto be shed following drought and thus on average are much youngerthan are established roots. Unlike previous measurements onroot respiration, lowering the gas-phase oxygen concentrationfrom 21% to 0% or raising the carbon dioxide concentration from0.1% to 2% had no detectable effect on Lp for rain roots andestablished roots. Lp for rain roots and established roots wasdecreased by an average of 11% and 35% by lowering the soilwater potential from wet conditions (soil=0 kPa) to {macron}40kPa and {macron}80 kPa, respectively. Such decreases in Lp mayreflect reduced water contact between soil particles and theroot surface and should be taken into account when predictingwater uptake by A. deserti. Key words: Gas phase, rain roots, root age, soil, temperature, water potential 相似文献
15.
Sugar Accumulation in Barley and Rice Grown in Solutions with low Concentrations of Oxygen 总被引:2,自引:0,他引:2
Barley and rice, at the early tillering stage, were grown inaerated nutrient solutions (> 7 mg O2 l1) and transferredto solutions of low O2 concentrations (< 0.5 mg l 1). For barley, low O2 concentrations during the first 5 days severelyinhibited growth of seminal roots had less effect on nodal roots,and did not reduce shoot growth. Longer exposure to low O2 concentrationsreduced shoot as well as root growth. Sugar concentrations inroots and shoots increased within 7 h after transfer of plantsto low O2 concentrations. After 5 days at low O2 concentrationssugar concentrations were very high in fast growing nodal rootsand in shoots, as well as in the slower growing seminal roots. In rice, low O2 concentrations increased sugar levels of rootsduring summer, but not during winter. In summer, the highersugar levels at low O2 concentrations persisted throughout adiurnal cycle. In root apices, sugar concentrations were increasedby low O2 concentrations, even though the experiment was donein winter and the bulk of the root system showed no differencein sugar levels. The data indicate that sugar accumulation, at low O2 concentrations,is caused by reduced growth and also that even apices of rootsgrown at low O2 concentrations have sufficient substrates forrespiration. Hordeum vulgare L, barley, Oryza sativa L, rice, sugar accumulation, oxygen concentration 相似文献
16.
A study was made of the incorporation of 14C by intact leavesof Coffea arabica (cultivars Mundo Novo, Catuai, 113013,and H 65862) and Coffea canephora (cultivar Guarini)supplied with gas mixtures containing 14CO2 under controlledconditions. Samples of the leaves were combusted and the 14Cin the CO2 produced measured using a liquid scintillation counter.The results were used to estimate photosynthetic rates. Theeffects of changing the partial pressures of O2 and CO2 on thephotosynthetic rate were studied and estimates made of the CO2compensation point and photorespiration. The data obtained show differences between the mean net photosyntheticrates of the C. arabica cultivars (6·14 mg CO2 dm2h1) and the mean rate for the C. canephora cultivar (3·96mg CO2 dm2 h1). The cultivar of the latter speciesphotorespired more rapidly than the cultivar Catuai of C. arabica.Rates of photosynthesis in coffee measured using the 14CO2 methodwere similar to rates obtained by others using an infrared gasanalyser. The 14CO2 method proved to be reliable for photosyntheticmeasurements and the apparatus is suitable for use in fieldconditions. 相似文献
17.
The influence of hydrogenase in Bradyrizobum-Phaseoleae symbioseswas studied ex-planta and in-planra in soybean (Glycine max)and cowpea (Vigna unguiculata). The hydrogenase was activatedby the addition of hydrogen in the incubation gas phase whichmodified the response of nitrogenase activity of Hup+ (hydrogenuptake positive) symbiosis to the external oxygen partial pressure.For bacteroids the hydrogenase expression increased nitrogenaseactivity at supraoptimal pO2, acting possibly as a respiratoryprotection of nitrogenase. However, at suboptimal pO2, nitrogenaseactivity of Hup+ bacteroids decreased with hydrogen, a phenomenonattributed to the lower efficiency of ATP synthesis from hydrogenthan from carbon substrates oxidation. For undisturbed nodules,the hydrogenase expression in soybean increased the optimalpO2 for ARA (COP), from 35.3 to 40.3 kPa O2, and the ARA atsupraoptimal pO2; at suboptimal PO2 there was a negative effectof hydrogenase on ARA, although this inhibition was less thanon bacteroids and was not detected if plants were grown at 15°C rather than 20 °C root temperature. No H2 effectwas detected on cowpea nodules. The results on soybean nodulesare consistent with the concept that symbiotic nitrogen fixationis oxygen-limited and that hydrogenase activity has no beneficialeffect on nitrogen fixation in O2 limitation. Key words: Glycine max, hydrogenase, nitrogenase, nitrogen fixation, nodules, Vigna unguiculata 相似文献
18.
The growth of four heathland species, two grasses (D. flexuosa,M. caerulea) and two dwarf shrubs (C. vulgaris, E. tetralix),was tested in solution culture at pH 4.0 with 2 mol m3N, varying the N03/NH4+ ratio up to 40% nitrate. In addition,measurements of NRA, plant chemical composition, and biomassallocation were carried out on a complete N03/NH4+ replacementseries up to 100% nitrate. With the exception of M. caerulea, the partial replacement ofNH4+ by NO3 tended to enhance the plant's growth ratewhen compared to NH4+ only. In contrast to the other species,D. flexuosa showed a very flexible response in biomass allocation:a gradual increase in the root weight ratio (RWR) with NO3increasing from 0 to 100%. In the presence of NH4+, grassesreduced nitrate in the shoot only; roots did not become involvedin the reduction of nitrate until zero ambient NH4+. The dwarfshrubs, being species that assimilate N exclusively in theirroots, displayed an enhanced root NRA in the presence of nitrate;in contrast to the steady increase with increasing NO3in Calluna roots, enzyme activity in Erica roots followed arather irregular pattern. Free nitrate accumulated in the tissuesof grasses only, and particularly in D. flexuosa. The relative uptake ratio for NO3 [(proportion of nitratein N uptake)/(proportion of nitrate in N supply)] was lowestin M. caerulea and highest in D. flexuosa. Whereas M. caeruleaand the dwarf shrubs always absorbed ammonium highly preferentially(relative uptake ratio for NO3 <0.20), D. flexuosashowed a strong preference for NO3 at low external nitrate(the relative uptake ratio for N03 reaching a value of2.0 at 10% NO3). The ecological significance of thisprominent high preference for NO3 at low NO3/NH4+ratio by D. flexuosa and its consequences for soil acidificationare briefly discussed. Key words: Ammonium, heathland lants, N03/NH4+ ratio, nitrate, nitrate reductase activity, soil acidification, specific absorption rate 相似文献
19.
Biochemical Limitations to Carbon Assimilation in C3 Plants--A Retrospective Analysis of the A/Ci Curves from 109 Species 总被引:9,自引:0,他引:9
Species-specific differences in the assimilation of atmosphericCO2 depends upon differences in the capacities for the biochemicalreactions that regulate the gas-exchange process. Quantifyingthese differences for more than a few species, however, hasproven difficult. Therefore, to understand better how speciesdiffer in their capacity for CO2 assimilation, a widely usedmodel, capable of partitioning limitations to the activity ofribulose-1,5-bisphosphate carboxylase-oxygenase, to the rateof ribulose 1,5-bisphosphate regeneration via electron transport,and to the rate of triose phosphate utilization was used toanalyse 164 previously published A/Ci, curves for 109 C3 plantspecies. Based on this analysis, the maximum rate of carboxylation,Vcmax, ranged from 6µmol m2 s1 for the coniferousspecies Picea abies to 194µmol m2 s1 forthe agricultural species Beta vulgaris, and averaged 64µmolm2 s1 across all species. The maximum rate ofelectron transport, Jmax, ranged from 17µmol m2s1 again for Picea abies to 372µmol m2 s1for the desert annual Malvastrum rotundifolium, and averaged134µmol m2 s1 across all species. A strongpositive correlation between Vcmax and Jmax indicated that theassimilation of CO2 was regulated in a co-ordinated manner bythese two component processes. Of the A/Ci curves analysed,23 showed either an insensitivity or reversed-sensitivity toincreasing CO2 concentration, indicating that CO2 assimilationwas limited by the utilization of triose phosphates. The rateof triose phosphate utilization ranged from 4·9 µmolm2 s1 for the tropical perennial Tabebuia roseato 20·1 µmol m2 s1 for the weedyannual Xanthium strumarium, and averaged 10·1 µmolm2 s1 across all species. Despite what at first glance would appear to be a wide rangeof estimates for the biochemical capacities that regulate CO2assimilation, separating these species-specific results intothose of broad plant categories revealed that Vcmax and Jmaxwere in general higher for herbaceous annuals than they werefor woody perennials. For annuals, Vcmax and Jmax averaged 75and 154 µmol m2 s1, while for perennialsthese same two parameters averaged only 44 and 97 µmolm2 s1, respectively. Although these differencesbetween groups may be coincidental, such an observation pointsto differences between annuals and perennials in either theavailability or allocation of resources to the gas-exchangeprocess. Key words: A/Ci curve, CO2 assimilation, internal CO2 partial pressure, photosynthesis 相似文献
20.
Hogan K.P.; Fleck I.; Bungard R.; Cheeseman J.M.; Whitehead D. 《Journal of experimental botany》1997,48(6):1289-1297
Red beech (Nothofagus fusca (Hook. F.) Oerst.; Fagaceae) andradiata pine (Pinus radiata D. Don; Pinaceae) were grown for16 months in large open-top chambers at ambient (37 Pa) andelevated (66 Pa) atmospheric partial pressure of CO2, and incontrol plots (no chamber). Summer-time measurements showedthat photosynthetic capacity was similar at elevated CO2 (lightand CO2-saturated value of 17.2 µmol m2 s1for beech, 13.5 µmol m2 s1 for pine), plantsgrown at ambient CO2 (beech 21.0 µmol2 s1,pine 14.9 µmol m2s1) or control plants grownwithout chambers (beech 23.2 µmol m2 s1,pine 12.9 µmol m2 s1). However, the higherCO2 partial pressure had a direct effect on photosynthetic rate,such that under their respective growth conditions, photosynthesisfor the elevated CO2 treatment (measured at 70 Pa CO2 partialpressure: beech 14.1 µmol m2 s1 pine 10.3)was greater than in ambient (measured at 35 Pa CO2: beech 9.7µmol m2 s1, pine 7.0 µmol m2s1) or control plants (beech 10.8 µmol m2s1, pine 7.2 µmol m2 s1). Measurementsof chlorophyll fluorescence revealed no evidence of photodamagein any treatment for either species. The quantity of the photoprotectivexanthophyll cycle pigments and their degree of de-epoxidationat midday did not differ among treatments for either species.The photochemical efficiency of photosystem II (yield) was lowerin control plants than in chamber-grown plants, and was higherin chamber plants at ambient than at elevated CO2. These resultssuggest that at lower (ambient) CO2 partial pressure, beechplants may have dissipated excess energy by a mechanism thatdoes not involve the xanthophyll cycle pigments. Key words: Carotenoids, chlorophyll fluorescence, photosynthesis, photoinhibition, photoprotection, xanthophyll cycle 相似文献